后6个数据点TLE，开了O2优化后变成了MLE，改了一个小时没改懂，请求指教

#include<iostream>
#include<queue>
#pragma GCC optimize(2)
using namespace std;

const int INF=0x3f3f3f;

int M[302][302];
bool map[302][302];
int m,x,y,t,xx,yy;

int dx[]={-1,0,1,0};
int dy[]={0,1,0,-1};

struct node{
	int x,y,step;
};

node nextt;
node now;

void BFS(int x,int y){
	queue<node>q;
	map[x][y]=1;
	now.x=x;now.y=y;now.step=0;
	q.push(now);
	while(!q.empty()){
		now=q.front();
		for(int i=0;i<4;i++){
			xx=now.x+dx[i];yy=now.y+dy[i];
			if(xx>=0&&yy>=0&&xx<=300&&yy<=300&&map[xx][yy]==0&&now.step+1<M[xx][yy]){//没走过 还没被炸 没越界 
				nextt.x=xx;nextt.y=yy;nextt.step=now.step+1;
				q.push(nextt);
				if(M[xx][yy]==INF&&xx>=0&&yy>=0){
					cout<<nextt.step;
					return;
				}
			}
		}
		q.pop();
	}
	cout<<"-1";
}

int main(){
	cin>>m;
	for(int i=0;i<=300;i++){
		for(int j=0;j<=300;j++){
			M[i][j]=INF;
		}
	}
	for(int i=0;i<m;i++){
		cin>>x>>y>>t;
		if(t<M[x][y])M[x][y]=t;//>0为不可经过 
		for(int j=0;j<4;j++){
			xx=x+dx[j],yy=y+dy[j];
			if(xx>=0&&yy>=0&&t<M[xx][yy])
				M[xx][yy]=t;
		}
	}
	BFS(0,0);
	return 0;
}